1. Field of the Invention
The invention relates to a diffusion-tight fluid conduit for hydrocarbon-containing fluids, in particular, fuels.
2. Description of the Related Art
Such fluid conduits are used primarily in the automotive industry. Especially in this field, ever higher requirements with regard to leakage of hydrocarbons, such as liquid fuels or brake fluid, be it as a result of defects, leaks, or diffusion to the exterior, as well as mechanical strength, corrosion resistance, heat resistance, fire resistance, and flexibility are posed.
In order to be able to fulfill as many of these requirements as possible, several solutions are known in practice as well as in the literature. Substantially, the fluid conduits, be they of a smooth or corrugated shape, are comprised of plastic pipes of most different materials, which are either reusable and/or can be decomposed naturally, of different layers of different materials and material mixtures, wherein one layer can also be of metal in order to achieve a-diffusion tightness or barrier with regard to diffusion as high as possible. Moreover, it is known to provide most different types of pipes of predetermined lengths at their ends with attached coupling members in order to connect them to a correspondingly matched coupling part connected to devices, pipes or hose.
These known solutions are generally complicated, difficult to manufacture and often still do not fulfill, or only partly fulfill, the requirements of the automotive industry.
From the U.S. Pat. No. 5,538,294 a substantially diffusion-tight fluid conduit is known which is in the form of a corrugated pipe of metal, which is corrugated at the inner and outer sides and exposed at the outer side, and two coupling members of metal which are connected by flanges or a screw connection to the ends of the corrugated pipe. Such a purely positive-locking connection is not sufficiently tight, especially not sufficiently diffusion-tight. The degree of corrosion resistance of the metal is not disclosed in this patent document. A corrugated pipe which is exposed to the fluid with its corrugated inner side increases the flow resistance and entails the risk that, after installation, particles contained in the fluid and/or liquid, such as condensed water or diesel fuel which can freeze at lower temperatures, will collect in the inner corrugation valleys of the corrugated pipe positioned at the bottom.
It is an object of the present invention to provide a fluid conduit for hydrocarbons, especially fuels, which makes it possible to fulfill to a very high degree most of the requirements posed by the automotive industry.
In accordance with the present invention, this is achieved in that the fluid conduit comprises a corrugated pipe of corrosion-resistant metal which is corrugated at its inner side and its outer side and is exposed at its outer side, a first coupling member connected to one end of the corrugated pipe by a material-bonding connection or additionally by a positive-locking connection so as to be seal-tight, and an inner pipe of plastic arranged within the corrugated pipe and having outer and inner smooth sides.
Material-bonding connections include, for example, fusing, welding, connections using adhesives, bonding agents etc., as is well known to a person skilled in the art.
Such a fluid conduit fulfills to a very high degree practically all of the requirements posed by the automotive industry. For example, the corrugated pipe is at least over its entire length completely diffusion-tight but also of high mechanical -strength, fire resistance, heat resistance, impact resistance, flexibility, and corrosion resistance. Since it is comprised of metal, it cannot be electrically charged by friction. Because of its high flexibility and the coupling member provided at least at one end, the fluid conduit can also be easily installed with different degrees of curvature and can be quickly connected by means of its coupling member to a matching coupling member, provided at a pipe socket of a device or the end of another fluid conduit, without the first coupling member having to be connected at the installation site with the corrugated pipe. When the first coupling member is also positive-lockingly connected to the corrugated pipe, the connection is especially strong. The smooth inner pipe of plastic material provides a corrugated pipe of a fluid conduit having corrugations at its inner and outer side with a smooth surface at its inner side which reduces the flow resistance in the fluid conduit and prevents the collection of particles and liquid in the lower corrugation valleys at the inner side of the corrugated pipe.
The first coupling member can also be comprised of corrosion-resistant metal. As an alternative, it can be comprised of a thermoplastic material.
Producing the coupling member of metal has the advantage that then the coupling member has an especially high diffusion tightness. On the other hand, thermoplastic material can be easily produced in the desired shape and can also be relatively diffusion-tight.
The metal of which the corrugated pipe or the first coupling member is comprised, can be stainless steel. This material is especially corrosion-resistant.
Preferably, it is provided that a second coupling member of corrosion-resistant metal, especially stainless steel, or thermoplastic material is connected to the other end of the corrugated pipe by a material-bonding connection or, additionally, by a positive-locking connection. In this embodiment, the two ends of the fluid conduit can be connected quickly with a corresponding coupling member of a pipe socket, a hose, or another pipe without having to connect the second coupling member with the corrugated pipe at the installation site.
The first coupling member or both coupling members can have a radial member surface which is connected with a radial pipe surface at the corresponding end of the corrugated pipe by a material-bonding connection. Such a connection is especially tight. When the coupling member or both coupling members are comprised of metal, they can be connected, for example, by welding to the corrugated pipe which is comprised of metal. However, it is also possible to connect the corrugated pipe with the coupling member or both coupling members by means of an adhesive. When one or both coupling members are comprised of thermoplastic material, they can also be connected to the corrugated pipe by means of a bonding agent between the radial surfaces in a seal-tight way.
Moreover, it can be ensured that the corrugated pipe has at each end connected to a coupling member a radially outwardly extending projection which, together with an end portion of the corrugated pipe and a portion of the coupling member adjacent to the end portion of the corrugated pipe, is embedded in a plastic ring by injection molding. This plastic ring can be provided alone or in addition to the described material-bonding connections and, in addition, makes possible a positive-locking connection by means of the projection which is embedded simultaneously when the end portion of the corrugated pipe is embedded by injection molding and, in this way, is positive-lockingly embedded in the thermoplastic material of the plastic ring.
The projection can be formed as a partial or complete circumferential flange. In the latter case a greater contact surface between the plastic ring and the flange results with a correspondingly higher sealing action.
When the plastic ring and the corrugated pipe are not connected by a material-bonding connection by means of a bonding agent, a sealing ring can be arranged between the plastic ring and the corrugated pipe.
Also, between the plastic ring and the coupling member or coupling members a sealing ring can be arranged when the plastic ring is not connected by a material-bonding connection to the coupling member or coupling members.
The inner pipe can have primarily a flexible thermoplastic material or a cross-linked rubber elastomer. Accordingly, the flexibility of the fluid line is not impaired by the addition of the inner pipe.
The plastic material of the inner pipe can also be mixed with electrically conducting particles, especially carbon black, in order to prevent a static electrical charge of the inner pipe by friction between the inner pipe and the fluid flowing therethrough.
Moreover, it can be ensured that an end portion of the coupling member or coupling members connected to the corrugated pipe is pressed into an end portion of the inner pipe. In this way, a relatively tight and strong connection results between the inner pipe and the coupling member.
When in this connection the end portion of the coupling member or coupling members is ribbed, the connection between the coupling member and the inner pipe provides a type of labyrinth seal since the material of the inner pipe can engage between the ribs of the ribbed end portion. In addition, this type of connection functions as a positive-locking connection.
Instead of plastic material, the inner pipe can also be comprised of a thin, flexible metal. This increases additionally the diffusion tightness without impairing the flexibility.
When the corrugated pipe has corrugations at its inner side and its outer side, it is especially flexible.
Moreover, the corrugated pipe can have smooth and corrugated portions. In this way, the fluid conduit can be produced with less material when it is clear from the beginning which portions of the fluid conduit must not be bent during installation. These portions can then be smooth, i.e., not corrugated.